Technical Field
Embodiments of the present invention relate to the field of display technologies, and particularly, to a pixel unit and a method for manufacturing the same, a display panel, and a display apparatus.
Description of the Related Art
Organic Light-Emitting Diode (OLED) device, due to its advantages including fully solid state construction, high brightness, full viewing angle, fast response time, broad working temperature range, flexible displaying and the like, becomes currently a younger generation display technology which is highly competitive and has a development prospect.
FIG. 1 shows a conventional process of manufacturing an OLED display apparatus. Firstly, array 102 of thin-film transistors (TFT) is manufactured on a flexible substrate 101, in which ITO pixel electrodes are separated by a pixel defining layer (PDL) 103 to define a pixel region; then, material 104 for light emitting layer and material 105 for negative electrode are deposited within the pixel region; and finally, subsequent processes are performed, to finish manufacture of the OLED display apparatus. Generally, material for light emitting layer comprises a Hole Injection Layer (HIL), a Hole Transport Layer (HTL), an Organic Layer, an Electron Transport Layer (ETL), and an Electron Injection Layer (EIL). In conventional process, the Hole Injection Layer (HIL), the Hole Transport Layer (HTL), the Electron Transport Layer (ETL), and the Electron Injection Layer (EIL), etc. are deposited mainly by means of using an open-type mask, material for the Organic Layer R, G, B is deposited by means of using a fine metal mask (FMM), and, material for negative electrode is usually deposited by means of using an open-type mask. In the subsequent processes, flexible packaging, i.e., thin film encapsulation (TEF), Dam &Fill, or adhesive+barrier film, is performed.
Material for the pixel defining layer is usually made of adhesive and has a thickness at micrometer-scale, while thicknesses of the materials for the light emitting layer and for the negative electrode deposited are of the order of magnitude of hundreds of nanometers. As a result, there is difference in height between material for the pixel defining layer and material for the light emitting layer as well as material for the negative electrode thereover. For a flexible OLED display apparatus, when the OLED display apparatus is bent, such difference in height between the pixel defining layer and the negative electrode likely causes phenomenon including fractures of the negative electrode or abscissions of the negative electrode from the pixel defining layer to occur at a stress concentration zone. Secondly, for flexible packaging, such as barrier film, Dam &Fill, and TFE, bubbles extremely likely occur at a position where there is difference in height between the pixel defining layer and the negative electrode, adversely affecting the package effect. These problems greatly adversely affect display effect of the display apparatus, and even cause failures of the display apparatus.